Water heaters that use solar energy are well known. Typically such heaters comprise a solar collector panel for heating up water and a water tank for storing the heated water prior to use. The panel is mounted on a roof with a sloping orientation such that the panel has an upper end and a lower end and is positioned so as to catch radiant energy from the sun. The panel is operatively coupled to a tank. Structurally the panel has a plurality of fluid ways extending between the upper and lower ends and the panel also has upper and lower headers communicating with the open ends of the fluid ways. The heater also has at least two conduits, eg located externally of the collector panel, coupling the panel to the tank. Specifically one said conduit couples the upper header with the tank and the other said conduit couples the tank with the lower header. Thus the heater overall facilitates water flow up through the fluid ways and into the tank.
In use solar energy from the sun heats up the panel by radiant heat transfer which in turn transfers heat to water in the fluid ways by convective and conductive heat transfer. This causes the water to expand and decrease in density causing it to travel up the fluid ways and into the upper header. From there the water passes into the tank for storage from where it is drawn for use when required. Within the tank the warmer water tends to move towards the top of the tank because of natural fluid convection within the tank. Inside the tank the cooler water is displaced by the warmer water to the bottom of the tank. A conduit links the bottom of the tank with the lower header and cooler water is drawn off the tank as freshly heated water from the upper header is introduced into the tank. This cooler water then passes from the lower header into the fluid ways where it is presented for heating in the manner described above and the cycle is repeated. This principle of circulating water through this heating system by natural convection is known as a thermosiphon effect and is well known. Using this system it is possible to heat water up to a temperature of 70° C. or even higher for use as domestic hot water for cleaning and washing.
This basic structure and principle of operation of the thermo-siphon effect has been described in many publications. Some such publications are AU 65934/94, AU 24885/95 and AU 15031/97. The contents of these specifications are hereby explicitly incorporated into the specification by direct cross reference.
However the heaters described above have some structural shortcomings. Firstly many solar collector panels comprise an assembly of pipes and sheets that is fabricated in a fairly elaborate metal working process. The fluid ways are made of pipes as are the headers and these have to be attached to each other, eg by welding or soldering. The pipes in turn are housed within a housing including a perimeter frame that has to be fabricated and the housing then has to be attached to the pipes. In addition couplings have to be provided for attachment of the external conduits to the headers in the panel. Finally a transparent cover sheet is mounted over the top of the pipes to reduce heat loss due to convection from the pipes. As a result the manufacture of the panel is fairly expensive.
In addition existing heaters also have some operational shortcomings. The pipes and headers are welded or soldered and these welds or solders are prone to failure when the piping is exposed to cold temperatures, eg frost conditions. The expansion of water in the pipes when it freezes causes these failures. The cost of repairing these welds or solders is substantial as the repairs need to be carried out by a qualified fitter usually on site.
A further operational shortcoming is that the metal pipes are susceptible to scale build up due to salts in the water such as calcium carbonate. This problem is well known in the boiler and water heater arts. While technology is available to resist this problem and/or clean the pipes the cost of de-scaling these pipes can be substantial. These above two operational shortcomings provide an incentive to move away from metal or steel pipes.
There is almost universal acceptance of the desirability of using solar heating to heat domestic water. It is a renewable energy source and reduces the reliance on electrical energy that is produced by coal fired power stations. This is recognised by many regulators and governments around the world. For example in Australia financial incentives in the form of rebates are offered to people installing solar hot water heating systems in their homes.
Applicant believes that the advantages of converting to solar heating are clear and that a major impediment to the widespread uptake of the technology is the capital cost of the existing systems and the maintenance problems described above. In particular the cost of a collector panel which is fabricated from metal is very high. Applicant believes that if these problems could be significantly reduced there would be a quantum increase in the uptake of the technology. Applicant believes that this would have the potential to make the use of solar heaters in domestic homes a standard feature in areas having high levels of sunlight.
Clearly therefore it would be advantageous if a lower cost solar heating system could be devised. Specifically it would be advantageous if a new and different way of manufacturing a solar collector panel could be devised that simplified the structure of the panel and reduced the cost of the panel.